Inflammatory myofibroblastic tumour (IMT) is a rare mesenchymal neoplasm that usually originates from abdominal soft tissues. A female patient aged 50 years presented with a 1.2 cm gallbladder polyp. The microscopic study showed spindle cell proliferation in an edematous background rich in lymphocytes and plasma cells. Immunohistochemistry showed positivity for vimentin, smooth muscle actin, and anaplastic lymphoma kinase (ALK), and negativity for other markers. Fluorescent in situ hybridization (FISH) revealed ALK gene rearrangement. The diagnosis was IMT of the gallbladder, a unique case considering that it was identified at the early stage of development of these neoplasms.

Keywords: gallbladder; soft tissue neoplasms; polyps.

INTRODUCTION

Inflammatory myofibroblastic tumour (IMT) is a rare mesenchymal neoplasm composed of myofibroblastic and fibroblastic spindle cells accompanied by an inflammatory infiltrate of plasma cells, lymphocytes, and/or eosinophilsPretas London black 005 2 Meus Fly Do Sexo Feminino Botas (1). It has been described, among other names, as inflammatory pseudotumor or plasma cell granuloma, but the designation of IMT was adopted by the 2013 World Health Organization (WHO) Classification of Tumours of the Soft Tissue and Bone(1). It has been sometimes mistaken for immunoglobulin G4 subclass (IgG4) related sclerosing disease; however, IMT is clinically and pathologically distinct(1-3). Expression of anaplastic lymphoma kinase (ALK) by immunohistochemistry is identified in 50%-60% of cases, and correlates well with the presence of ALK gene rearrangement(1). The clonal presence of this alteration has been very useful in classifying IMT as a distinct entity, as well as a true neoplasmDo London Sexo 2 005 Feminino Pretas black Botas Fly Meus (1, 4-6).

IMT primarily affects children and young adults, with mean age of 10 years, although the age range stretches throughout adulthood(1). It can arise in any organ, but occurs most frequently in the mesentery, omentum, retroperitoneum, pelvis, and abdominal soft tissues(1). Gastrointestinal locations are unusual(1, 7), and regarding primary IMT of the gallbladder, only a few well documented and convincing cases can be found in the literature(8-11), all of them describing large lesions. In this report, we describe a unique case of primary IMT of the gallbladder, considering that it was diagnosed at the early stage of development of these neoplasms.

CASE REPORT

Clinical data

A 50-year-old female patient, with no previously known diseases, presented with a gallbladder polypoid lesion on a routine abdominal ultrasound, identified as hypervascular by Doppler study. A laparoscopic cholecystectomy was carried out.

The characteristics of the antibodies used for the immunohistochemistry study are summarized in Table. Studies were performed on one representative block of the lesion, resorting to the avidin-biotin-peroxidase complex detection system and performed on a Ventana Marker Platform Bench Mark ULTRA IHC/ISH.

The tumour was diagnosed as primary IMT of the gallbladder, associated with ALK gene rearrangement.

Botas 2 005 Do London Feminino Sexo black Pretas Fly Meus DISCUSSION

IMT is a rare mesenchymal neoplasm, with a very limited number of cases of primary of the gallbladder reported in the literature(8-11).

The site of origin determines the symptoms and the abdominal tumours are known for causing gastrointestinal obstruction(1). Up to one third of the patients present clinical syndrome of fever, malaise, weight loss, and laboratory abnormalities that disappear after mass excision(1, 6, 12). In our case, the patient was asymptomatic and the tumour was detected during a routine abdominal ultrasound.

Grossly, IMT is usually a nodular, circumscribed or multinodular mass, with a tan, whorled, fleshy or myxoid cut surface appearance, with variable hemorrhage, calcification or necrosis; it can measure between 1 cm and 20 cm(1, 6).

Histologically, the neoplastic cells form three basic patterns(1, 6, 12). The first closely mimics a reactive process similar to granulation tissue, characterized by loosely arranged plump or spindle myofibroblasts in an oedematous background with abundant blood vessels and an infiltrate of plasma cells, lymphocytes and eosinophils(1, 6, 12). The second pattern, in which our case is included, consists of a more compact spindle cell proliferation with variable myxoid and collagenized stroma accompanied by the same inflammatory infiltrate(1, 6, 12). However, we did not observe ganglion-like myofibroblastic cells, described as frequent in this pattern. The third pattern consists of a scar-like proliferation with dense collagen fibers, low myofibroblastic cellularity and sparse inflammatory infiltrate(1, 6, 12).

This tumour shows positivity for vimentin and variable staining for SMA, muscle specific actin (HHF35) and desmin(1, 6). Focal keratin expression can be identified, as well as CD68 in histiocyticappearing cells(1). Cytoplasmic expression of ALK is present in 50%-60% of cases and correlates well with the presence of ALK gene rearrangement (1), as seen in our case.

IMTs are genetically heterogeneous, probably because of the different entities grouped in this category(1). ALK gene rearrangements are more uncommon in patients above 40 years(1), making this case even more unusual due to the presence of this rearrangement. The presence of clonal cytogenetic rearrangements has been a strong factor in classifying this entity as neoplastic rather than a reactive process(1, 5, 6, 13). The recurrence rate of extrapulmonary IMT can reach 25%, and is related to factors such as anatomic site, resectability and multinodularity(1). Metastases are rare, generally occurring in less than 2% of cases(1). A more aggressive clinical behavior has been reported to be associated with the presence of round cell morphology with membrane or perinuclear pattern of ALK immunohistochemical staining and RANBP2-ALK rearrangement(14, 15) or with ALK-negative IMT(6, 16). However, especially in patients with intra-abdominal tumours, a benign behavior of ALK-negative IMT is observed, including spontaneous regression(17).

Crizotinib (Xalkori®, made by Pfizer, Inc.), a tyrosine kinase inhibitor approved by the Food and Drug Administration (FDA) for the treatment of advanced lung cancer with ALK rearrangementsblack Sexo Do Meus 2 Feminino Pretas London 005 Botas Fly (18, 19), has been reported to be potentially useful in cases of aggressive IMT(20).

In our case, the excision was complete, due to the unique characteristics of this tumour regarding the small size and location within the gallbladder. The patient has been in clinical follow-up for 12 months, with no signs of recurrent disease.